Photoluminescence Of Nanoparticles Research Articles

Improving the photoluminescence of CeO2 nanoparticles via creating oxygen vacancies in the crystal lattice

Cerium oxide (CeO2) is a type of crystal semiconductor that's been getting a lot of attention lately because of its optical features, notably photoluminescence (PL). CeO2 nanoparticles can emit strong blue PL bands upon excitation by UV light (λ = 325), therefore, it can be utilized as a phosphor. Therefore, this study aims to enhance the utilization of cerium oxide as a phosphor in a broad range of industrial applications, by achieving multiple emissions in visible regions to facilitate its use in minimized costs in the various applications. In the context of the present study, an attempt to improve the usually emitted blue PL spectra of CeO2 was performed through CeO2 nanoparticles were subjected to thermal reduction in hydrogen environment at elevated temperatures (200–1000 °C). The obtained reduced samples were analyzed by using a variety characterization methods, including XRD, UV-Vis, SEM, XPS and HR-TEM. Characterization data showed that several oxygen vacancies are formed in the CeO2 lattice. The PL of the reduced CeO2 was investigated under different excitation wavelengths in the ultra-violet region (325, 345, 369, and 390 nm). It was found that the photoluminescence spectra of the original CeO2 sample either shifted or disappeared after thermal reduction. More importantly, new PL spectra in the wavelength range of 540 and 560 nm (greenish yellow) were observed. The intensity of these spectra was found to be increased with increasing the reduction temperature. The obtained results confirmed the possibility of obtaining different emitting PL spectra with several colors upon UV excitation compared to bare CeO2 nanoparticles. Therefore, reduced ceria can be used as a multi-color phosphor in several applications such as banknote watermarks.

Metallic photoluminescence of plasmonic nanoparticles in both weak and strong excitation regimes

Abstract The luminescent nature of plasmonic nanoparticles (NPs) has been intensively investigated in recent years. Plasmon-enhanced electronic Raman scattering and the radiation channels of metallic photoluminescence (PL) involving conventional carrier recombinations and emergent particle plasmons are proposed in the past few decades but largely limited to weak excitation regimes. Here, we systematically examine the PL evolution of plasmonic NPs under different excitation power levels. The spectral resonances and chromaticity of PL are investigated within and beyond the scope of geometry conservation. Results indicate the nature of PL in plasmonic NPs could be a process of graybody radiation, including one factor of plasmonic emissivity in the weak excitation regime and the other factor of blackbody radiation in the strong excitation regime. This comprehensive analysis provides a fundamental understanding of the luminescent nature of plasmonic NPs and highlights their potential applications in transient temperature detection at the nanometer scale.

Quantum dot-based lateral flow immunoassay for the rapid detection of pathogens

On October 4, 2023, the Nobel Prize in Chemistry was awarded to Moungi Bawendi, Louis Brus, and Aleksey Yekimov for the discovery and synthesis of quantum dots (QDs). The Nobel Foundation credited QDs as being the “seeds of nanoscience”. As suggested by its name, QDs are extremely small matter resembling a dot. A QD is a photoluminescent nanoparticle composed of semiconductor materials with diameters ranging between 2 and 10 nm. It often consists of only a few thousand atoms and are smaller than human cells and viruses [1,2].

Chameleon-like Photoluminescent Janus Nanoparticles as Full-Color Multicomponent Organic Nanoinks: Combination of Förster Resonance Energy Transfer and Photochromism for Encryption and Anticounterfeiting with Multilevel Authentication.

Increasing the security by the multilevel authentication mechanism was the most significant challenge in recent years for the development of anticounterfeiting inks based on photoluminescent nanomaterials. For this purpose, the greatest strategy is the use of multicomponent organic materials and a combination of Förster resonance energy transfer (FRET) with the intelligent behavior of photochromic compounds like spiropyran. Here, the hydroxyl-functionalized polymer nanoparticles were synthesized by emulsion copolymerization of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) in different compositions (0-30 wt % of HEMA). Results illustrated that the size of the nanoparticles changed from 64 to 204 nm, and a morphology evolution from spherical to Janus shape was observed by increasing the concentration of HEMA. Photoluminescent inks with red, green, and blue (RGB) fluorescence emissions were prepared by modification of nanoparticles containing 15 wt % of HEMA with spiropyran, fluorescein, and coumarin, respectively. To develop dual-color and multicolor photoluminescent inks that display static and dynamic emission, RGB latex samples were mixed together in different ratios and printed on cellulosic paper. Results display that the fluorescence emission of developed inks can be photoswitched between different statuses, including white to blue, green to blue, green to red/orange, purple to pink, and white to pink, utilizing the FRET phenomenon, photochromism, and a combination of both phenomena. Samples containing spiropyran displayed dynamic color changes in the emission to red, orange, and pink depending on the composition. Hence, developed dual-color and multicolor photoluminescent inks were used for printing of security tags and also painting of some hand-drawn artworks, which obtained results indicating high printability, maximum fluorescence intensity, high resolution, and fast responsivity upon UV-light irradiations of 254 nm (for static mode) and 365 nm (for dynamic mode). In addition, the multilevel authentication mechanism by a static emission under UV-light irradiation of 254 nm, a dynamic emission under UV-light irradiation of 365 nm, and photochromic color change was observed, resulting in increasing the security of developed inks. Actually, developed multicolor photoluminescent inks are the most efficient candidates for developing a new category of chameleon-like high-security anticounterfeiting inks that have tunable optical properties and complex multilevel authentication mechanisms.

Tetraphenylethylene-Based Photoluminescent Self-Assembled Nanoparticles: Preparation and Biological Evaluation.

The conjugation of tetraphenylethylene (TPE) with podophyllotoxin, N-desacetylthiocolchicine, and cabazitaxel through a sebacic acid linker led to the formation of fluorescent nanoparticles. Dynamic light scattering (DLS) and photoluminescence spectroscopy were used for the identification and characterization of the fluorescent nanoparticles. The biological evaluation was determined in three human ovarian (KURAMOCHI, OVCAR3, OVSAHO) and three human breast (MCF7, SKBR 3, and MDA-MB231) cancer cell lines. In the case of cabazitaxel, the nanoparticles maintained the activity of the parent drug, at the low nanomolar range, while exhibiting high blue fluorescence. The internalization of the fluorescent NPs into cells was detected using immunofluorescence assay.

Theoretical and Experimental Study of Optical Losses in a Periodic/Quasiperiodic Structure Based on Porous Si-SiO2

This study investigates the reduction of optical losses in periodic/quasiperiodic structures made of porous Si-SiO2 through a dry oxidation process. Due to their unique optical properties, these structures hold great promise for various optoelectronic applications. By carefully engineering the composition and geometry of the structures, we fabricate periodic/quasiperiodic structures on a quartz substrate using an electrochemical anodization technique and subsequently subject them to dry oxidation at two different temperatures. The structure exhibits two localized modes in the transmission and reflection spectra. Unoxidized and oxidized structures’ complex refractive index and filling factors are determined theoretically and experimentally. Optical characterization reveals that the porous Si-SiO2 structures exhibit lower absorption losses and improved transmission than the pure porous silicon structures. Additionally, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) confirm the presence of porous Si-SiO2 and reduced silicon content. Our study demonstrates that dry oxidation effectively decreases Rayleigh scattering losses, leading to enhanced optical performance and potential applications in efficient optoelectronic devices and systems based on silicon. For instance, periodic/quasiperiodic structures could soon be used as light-emitting devices inside the field of optoelectronics, adding photoluminescent nanoparticles to activate the localized modes.

5-Fluorouracil-loaded designed praseodymium oxide – poly- β-cyclodextrin nanorods for effectively inhibiting breast cancer cells

Breast cancer remains one of the commonly prevailing and challenging diseases. Lanthanide-based nanomaterials are fascinating depending on their unique properties and represent a preferable choice of drug transport, aimed at finding an agent for targeted therapy. It necessitates that lanthanide-based nanocarriers with suitable surface modification and desired physicochemical characteristics are developed for effective anticancer drug delivery, owing to their fascinating light absorption, magnetic, and morphological features. Herein, we report praseodymium oxide nanorods in combination with poly-cyclodextrin as a novel nanocarrier to deliver the chemotherapeutic drug 5-fluorouracil to breast cancer cells. The praseodymium oxide nanoparticles were prepared using a sonochemical method and characterized using routine analytical methods, including X-ray Diffraction, Transmission Electron Microscopy, and X-ray Photoelectron Spectroscopy. The monodisperse rod-shaped structures possess length and width of 200 ± 30 and 72 ± 10 nm, respectively. The nanoparticles are 64.33% crystalline, revealed by XRD. The polymer content in the nanoparticles is ∼37% by weight. Further, the nanoparticles' magnetic, light absorption and photoluminescence characteristics are studied. Low saturation magnetization and insignificant hysteresis properties are observed. Broad absorption and visible wavelength region photoluminescence arise from the praseodymium in the material. The continuous release of the drug cargo and the in vitro anticancer activity are discussed. The loaded drug (5-fluorouracil) is released sustainably, extending over 250 hours. The anticancer activity in vitro is observed with the portion of the drug released from the nanocarrier. The apoptotic action mode of the drug-carrier vehicle is analyzed. The inhibition of cells occurs mainly on the S-phase of the cell cycle. The nanomaterial can function as a drug carrier and is suitable for anticancer therapy. The results reported herein on praseodymium oxide nanoparticles are promising as a nanocarrier and pose the possibility of future in vivo studies.

Multicolor Photoluminescence from Nonconjugated Poly(3,4-dihydropyran) Nanoparticles

In recent years, nonconjugated organic luminophores are receiving considerable interest from the scientific community, offering a new conceptual basis for the development of alternative photoluminescence-based technologies. In this work, the polymerization of 3,4-dihydropyran was exploited for the preparation of nonconjugated photoluminescent polymer nanoparticles. Remarkably, excitation-dependent multicolor emission ranging from blue to yellow was observed in both solid and solution. In contrast with similar materials, this behavior was not attributed to aggregation-induced emission, but rather to the presence of independent, noninteracting chromophores located on the polymer structure. Structural and optical characterizations along with further chemical modifications suggest that the emission is related to the presence of acetal groups formed by ring-opening polymerization. In addition, it was shown that the removal of unsaturated structures could enhance the photoluminescence quantum yield of the polymer (QY) up to 0.20 (λex = 355 nm). This work provides a new type of nonconjugated organic luminophore with both high QY and multicolor emission.

Влияние электрического поля на рекомбинационную люминесценцию коллоидных квантовых точек сульфида серебра

The paper studies the effect of external electric field on the optical properties of the spherical Ag2S quantum dots. Colloidal Ag2S nanoparticles passivated with 2-mercaptopropionic acid were obtained by photoinduced synthesis in the ethylene glycol. The nanoparticles shape and characteristic size were determined using the transmission electron microscopy. To analyze the external electric field influence, a series of samples was prepared based on the optically passive polymer film, where the nanoparticles were embedded. The films were placed between two glasses coated with the transparent electrodes based on the indium tin oxide (ITO). Intensity value of the external electric field created in such structures reached 500 kV/cm. The photoluminescence signal was registered using the CCD fiber spectrometer with spectral resolution of 1.16 nm. Spectrally resolved nanoparticles photoluminescence kinetics was measured by time-corre-lated counting of the separate photons. It was found that the presence of a field led to an increase in intensity and rate of the photoluminescence relaxation due to the surface states. This fact is related to acceleration of the free holes transportation to the recombination centers in the external electric field. It is shown that under long-term exposure to laser radiation with a wavelength of 405 nm and the average power of 5 mW, the nanocrystal photoluminescent properties could degrade, as it occurs due to formation of new centers of non-radiative recombination and photoionization of the quantum dots

Supramolecular Chemistry of Carbon-Based Dots Offers Widespread Opportunities.

Carbon dots are an emerging class of nanomaterials that has recently attracted considerable attention for applications that span from biomedicine to energy. These photoluminescent carbon nanoparticles are defined by characteristic sizes of <10 nm, a carbon-based core and various functional groups at their surface. Although the surface groups are widely used to establish non-covalent bonds (through electrostatic interactions, coordinative bonds, and hydrogen bonds) with various other (bio)molecules and polymers, the carbonaceous core could also establish non-covalent bonds (ππ stacking or hydrophobic interactions) with π-extended or apolar compounds. The surface functional groups, in addition, can be modified by various post-synthetic chemical procedures to fine-tune the supramolecular interactions. Ourcontribution categorizes and analyzes the interactions that are commonly used to engineer carbon dots-based materials and discusses how they have allowed preparation of functional assemblies and architectures used for sensing, (bio)imaging, therapeutic applications, catalysis, and devices. Using non-covalent interactions as a bottom-up approach to prepare carbon dots-based assemblies and composites can exploit the unique features of supramolecular chemistry, which include adaptability, tunability, and stimuli-responsiveness due to the dynamic nature of the non-covalent interactions. It is expected that focusing on the various supramolecular possibilities will influence the future development of this class of nanomaterials.

Photosensing of chain polarity and visualization of latent fingerprints by amine-functionalized polymer nanoparticles containing oxazolidine

Here, the photoluminescent amphiphilic nanoparticles were synthesized by doping of the hydroxylated oxazolidine derivative as a highly fluorescent organic chromophore to the surface of functionalized copolymer nanoparticles containing amine groups. Prepared amphiphilic copolymer nanoparticles have variable particle sizes in the range of 58–1320 nm with various spherical morphologies depending on the concentration of 2-(dimethylamino)ethyl methacrylate (DMAEMA). Investigation of optical properties for constructed photoluminescent amphiphilic nanoparticles indicated photoinduced electron transfer (PET) phenomenon between tertiary amine groups of DMAEMA and oxazolidine molecules. The photoluminescent polymer powder samples were used for printing of encrypted information on cellulose papers by powder dusting method. Printed quick responsive (QR) codes have fluorescent emission in various colors with maximum resolution, intensity, and brightness under UV-light irradiation of 365 nm. In addition, the visualization of fingerprints by powder dusting and fluorescence imaging under UV-light irradiation (365 nm) was carried out by using photoluminescent polymer powders. The fingerprints are detectable by photoluminescent nanomaterials in a rapid and accessible manner, and all three levels of identification for fingerprint ridge patterns are achievable. Therefore, developed photoluminescent nanomaterials can offer authoritative evidence for the encryption of information, and also recognize the individual identity in a short time and with the least facilities.

Photodegradation of methylene blue dye using light driven photocatalyst-green cobalt doped cadmium ferrite nanoparticles as antibacterial agents

A cobalt-doped cadmium ferrite nanoparticle (CoxCd1-xFe2O4; x = 0, 0.2, 0.4, 0.6, 0.8, 1) was synthesized using curd as fuel during combustion. The symphonized nanoparticle's crystalline structure, size, morphology, photoluminescence, and optical properties are analyzed using PXRD, FTIR, SEM, HRTEM, XPS, UV–visible, and photoluminescence spectroscopies. PXRD analysis indicates that synthesized nanoparticles have a cubic spinel structure and that as cobalt doping increases, crystalline size and the lattice parameter decrease. FTIR analysis confirms tetrahedral and octahedral sites for vibrational stretching modes. Further SEM and HRTEM analyses reveal the morphology of the synthesized nanoparticles, which are agglomerated and have a nanoflakes-like structure. Furthermore, X-ray photoelectron spectroscopy reveals the elemental composition, oxidation, and transition states of CDCF NPs. UV–Vis spectroscopy discloses absorption, band gap regarding prepared NPs, and band gap deductions with increased cadmium substitution. The effect of cadmium substitution on luminescence is demonstrated by photoluminescence spectroscopy. Under visible light, photodegradation of the dye Methylene Blue in the presence of photocatalyst CDCF nanoparticles indicates that Co0.4Cd0.6Fe2O4 has higher degradation activity than other NPs. Antibacterial activity was performed for Gram-positive (S. aureus) and Gram-negative (Shigella) in the presence of synthesized Nano-particles. Activity results revealed that Co0.6Cd0.4Fe2O4 and CO0.2Cd0.8Fe2O4 NPs show an excellent zone of inhibition for S. aureus and Shigella bacterial strains.

Photoluminescent Scaffolds Based on Natural and Synthetic Biodegradable Polymers for Bioimaging and Tissue Engineering.

Non-invasive visualization and monitoring of tissue-engineered structures in a living organism is a challenge. One possible solution to this problem is to use upconversion nanoparticles (UCNPs) as photoluminescent nanomarkers in scaffolds. We synthesized and studied scaffolds based on natural (collagen-COL and hyaluronic acid-HA) and synthetic (polylactic-co-glycolic acids-PLGA) polymers loaded with β-NaYF4:Yb3+, Er3+ nanocrystals (21 ± 6 nm). Histomorphological analysis of tissue response to subcutaneous implantation of the polymer scaffolds in BALB/c mice was performed. The inflammatory response of the surrounding tissues was found to be weak for scaffolds based on HA and PLGA and moderate for COL scaffolds. An epi-luminescent imaging system with 975 nm laser excitation was used for in vivo visualization and photoluminescent analysis of implanted scaffolds. We demonstrated that the UCNPs' photoluminescent signal monotonously decreased in all the examined scaffolds, indicating their gradual biodegradation followed by the release of photoluminescent nanoparticles into the surrounding tissues. In general, the data obtained from the photoluminescent analysis correlated satisfactorily with the histomorphological analysis.

Photochromic polymer nanoparticles as highly efficient anticounterfeiting nanoinks for development of photo-switchable encoded tags

• Synthesis of colloidal nanoparticles with different polarity and particle size, • Preparation of spiropyran-containing photochromic colloidal nanoparticles, • Effect of polarity on the fluorescence emision and photochromism of colloidal nanoparticles, • Development of the photochromic colloidal nanoparticles as anticounterfeiting nanoinks, • Application of the smart nanoinks for encrypting security documents. Dual photochromic and photoluminescent latex nanoparticles were synthesized to develop innovative anticounterfeiting nanoinks with applications in encryption technology. The colloidal nanoparticles bearing hydroxyl groups were resulted from semi-continuous miniemulsion copolymerization of 2-hydroxyethyl methacrylate and methyl methacrylate. Investigation of the particle size determination and microscopic analysis results demonstrated spherical morphologies for the latex nanoparticles with a mean size of about 80 nm and narrow size distribution. Modification of the polymer nanoparticles with hydroxyl functional groups led to the formation of a high level of hydrogen bonding between the hydroxyl groups and spiropyran chromophore, which is an advantage in the preparation of security anticounterfeiting nanoinks. In addition, optical analysis of the photochromic latex samples showed various UV-vis spectra, fluorescence emission, kinetics of isomerization, and photo-fatigue resistance depending on different amounts of the polar monomers. Further investigations on optical properties exhibited that reducing the size of the colloidal samples can affect their photoluminescence characteristics. This is an efficient way to provide remarkable photoreversible anticounterfeiting inks for different applications, such as printed photo-marking, rewritable handwriting patterns, security encoded tags, and labeling.

Amplifying Photoluminescence of Lanthanide-Doped Nanoparticles by Iridium Phosphonate Complex

Amplifying the photoluminescence of lanthanide-doped nanoparticles by antenna materials can bridge the gap in properties between pristine nanoparticles and those required by practical applications. However, high-performance antennas with ideal stability are rather few. Here, we report a new type of iridium (Ir)-based phosphonate complex as an antenna to amplify the near-infrared luminescence of lanthanide-doped nanoparticles. Unlike conventional antennas, the Ir complex, with a quasi-spherical structure and pendent phosphonic groups, can resist the aggregation-caused quenching and firmly anchor on nanoparticles. Near-infrared luminescence of lanthanide-doped nanoparticles can be stably amplified up to 130 times by the complex, which should be due to short-range energy transfer from the triplet state of the complex to lanthanide ions. These findings may pave a new fundamental way to amplify the luminescence of lanthanide-doped nanoparticles and promote applications of the nanoparticles.

All-in-one photoluminescent Janus nanoparticles for smart technologies: Organic light-emitting diodes, anticounterfeiting, and optical sensors

In this study, a new category of amphiphilic nanoparticles based on random copolymers was prepared by polymerization of the methyl methacrylate (MMA) with methacrylamide (MAAm) in emulsion media to develop functionalized nanoparticles containing amide polar groups in different concentrations, and also the size of nanoparticles is in the range of 47–145 nm. Subsequently, the physical modification of amide groups on the surface of functionalized amphiphilic nanoparticles by using oxazolidine derivative (OXOH) with a concentration of 5 wt% led to the development of photoluminescent copolymer nanoparticles (PLCNPs). The MAAm monomer was used to functionalize polymer nanoparticles with amide groups acting as electron donor groups for oxazolidine molecules and their stability on the surface of the polymer nanoparticles by hydrogen bonding. To investigate of optical properties, the PLCNPs samples containing different concentrations of amide groups (0–20 wt%) were studied by photoluminescence and UV–Vis spectroscopy. Obtained results indicate that the emission and absorbance bands (intensity and wavelength) can be influenced significantly by the concentration of amide groups located on the surface of amphiphilic nanoparticles, and most importantly the local polarity. Investigation of the color change of photoluminescence emission for PLCNPs samples as a function of amide group concentration by CIE colorimetric diagrams displayed regular shifts in color position by the increase of local polarity, which observed color shifts are in agreement with results of photoluminescence and UV–Vis spectra. It was observed that PLCNPs samples displayed suitable adhesion to the surface and stable optical properties when deposited or coated on substrates that have polar surfaces, such as thermoset/thermoplastic polymer sheets and also cellulose papers. Hence, the PLCNPs samples were used directly as the colloid solution to develop photoluminescence organic light emitting diodes, water-based and ecofriendly anticounterfeiting inks, and the portable sensor for the detection of artificially created scratches on the surface of the polycarbonate sheet by fluorescence imaging. The results displayed that printed security tags and encrypted information on cellulose papers have orange fluorescence emission with remarkable intensity because the size of latex particles is in the range of nanoscale (below 100 nm) which led to a reduction of light scattering and an increase of light absorption. In a new approach and for the first time, a solution of poly(vinyl alcohol) (PVA)/PLCNPs was deposited on LED (has blue light emission with a wavelength of 365 nm) to change the color of photoluminescence emission from blue to orange-purple by excitation of an organic photoluminescent polymer layer with UV light of LED (365 nm). On the other hand, the PLCNPs solutions were sprayed on the substrate to detect created scratches on the polycarbonate sheet under irradiation with UV light (365 nm) and fluorescence imaging. The advantages of developed water-based PLCNPs samples resulted in to use as an all-in-one nanomaterial in a different and wide range of applications, such as photoluminescent inks for ecofriendly anticounterfeiting technologies, photoluminescence OLEDs, and also a portable detector for optical visualization of scratches and micro-cracks on various substrates.

Dual-Color Photoluminescent Functionalized Nanoparticles for Static-Dynamic Anticounterfeiting and Encryption: First Collaboration of Spiropyran and Coumarin.

Increasing the security of anticounterfeiting materials has been the most important challenge in recent years, and the development of dual-color photoluminescent inks with multi-level security, static/dynamic emission, and dynamic color change is an important solution to overcome this problem. In this study, the multi-functionalized copolymer nanoparticles containing different functional groups (with a concentration of 20 wt %), including ester, carboxylic acid, hydroxyl, epoxide, amide, and amine groups were synthesized successfully by the emulsion polymerization method. The results showed that the particle size and morphology of nanoparticles are affected by the polarity of functional groups. The prepared multi-functionalized copolymer nanoparticles were modified physically with spiropyran (photochromic and red fluorescence emission) and coumarin (cyan emission) derivatives to develop dual-color photoluminescent polymer nanoparticles with application in static-dynamic photoluminescent anticounterfeiting inks, which have multi-level security. The investigation of optical properties indicates that the kinetics of photochromism and photoluminescence properties of samples containing spiropyran is dependent on the local polarity on the surface of polymer nanoparticles. Hence, an increase in the polarity (functionalization with amide, carboxylic acid, and hydroxyl groups) has resulted in fast photochromism, high-intensity photoluminescence emission and increased the efficiency of the photoswitchable color change of emission from cyan to pink. Dual-color photoluminescent anticounterfeiting inks were prepared by mixing polymer nanoparticles containing spiropyran with polymer nanoparticles containing coumarin, in different ratios (1:1, 1:3, 1:5, 1:8, and 1:10). Obtained results showed that prepared samples have cyan emission under UV light of 254 nm (static mode), and a dynamic photoswitching of fluorescence emission from cyan to pink (as a function of irradiation time) was also observed under UV-light irradiation of 365 nm, which is well known as a dynamic mode of emission. The responsivity and intensity of dynamic photoluminescence emission are dependent on the local polarity of the surface functional groups, in which the samples based on amide functionalized copolymer nanoparticles displayed high-intensity emission in the static mode and high-intensity photoswitchable dual-color emission in the dynamic mode, in the case of all ratios of colloid solution mixtures. Printing security tags on cellulose paper by dual-color photoluminescent inks indicates advantages such as maximum printability, resolution, brightness, and static-dynamic photoluminescence emission with high intensity for inks based on amide functionalized nanoparticles. The static-dynamic dual-color photoluminescent anticounterfeiting ink with unique properties and multi-level security was reported for the first time by the collaboration of spiropyran and coumarin. This study can open a new approach and window to the future of advanced and high-security anticounterfeiting technologies.

Single-Particle Photoluminescence and Dark-Field Scattering during Charge Density Tuning.

Single-particle spectroelectrochemistry provides optical insight into understanding physical and chemical changes occurring on the nanoscale. While changes in dark-field scattering during electrochemical charging are well understood, changes to the photoluminescence of plasmonic nanoparticles under similar conditions are less studied. Here, we use correlated single-particle photoluminescence and dark-field scattering to compare their plasmon modulation at applied potentials. We find that changes in the emission of a single gold nanorod during charge density tuning of intraband photoluminescence can be attributed to changes in the Purcell factor and absorption cross section. Finally, modulation of interband photoluminescence provides an additional constructive observable, giving promise for establishing dual channel sensing in spectroelectrochemical measurements.

Solvent-free synthesis of photoluminescent carbon nanoparticles from lignin-derived monomers as feedstock

ABSTRACT Photoluminescent carbon nanoparticles (CNPs), such as carbon dots (CDs), have attracted much attention owing to a unique set of properties, like high and tunable fluorescence. In this way, the use of carbon-rich lignin has been demonstrated to be a sustainable approach to producing a broad range of photoluminescent CNPs. However, the valorization of this complex polyphenol is limited when it comes to green and efficient ways of conversion. In addition, the existing solvothermal approaches using lignin often result in CDs with low photoluminescence, while flammable and/or toxic solvents are employed. Here, we depolymerized technical lignins, i.e. kraft and soda, through electroreductive cleavage in two different sustainable media: deep eutectic solvent and levulinic acid. After depolymerization, lignin-derived monomers were generated, with a predominance of aryl ether and phenolic groups, which were further combined with 1,2-Phenylenediamine to produce N-doped CNPs in a solvent-free approach. Photoluminescent CNPs with varied sizes were generated (5–50 nm), which presented a wide photoluminescence emission, from blue to red, depending on solvent polarity. These results demonstrate a feasible and sustainable route for the solvent-free synthesis of photoluminescent CNPs using lignin-derived monomers as carbon source, which may find applications in a wide range of fields.

Photoluminescent Janus oxazolidine nanoparticles for development of organic light-emitting diodes, anticounterfeiting, information encryption, and optical detection of scratch.

Photoluminescent polymer nanoparticles based on organic compounds are a new category of advanced materials with potential applications in various fields such as chemosensors, optical devices, drug-delivery systems, anticounterfeiting inks and bioimaging. Herein, amide functionalized copolymer nanoparticles with a particle size in the range of 42-139nm were synthesized by emulsion copolymerization of methylmathacrylate (MMA) and methacrylamide (MAAm) with different concentrations in the range of 0-20wt%. Afterward, the photoluminescent copolymer nanoparticles (PLCNPs) were prepared by physical modification of amide functionalized copolymer nanoparticles with 5wt% of oxazolidine derivative (OXOH). Investigation of optical properties include of photoluminescence and UV-vis spectra displayed significant dependency of emission and absorbance bands to the local polarity or the concentration of the amide groups on the surface of the nanoparticles. Study of Commission Internationale de l'Eclairage (CIE) colorimetric diagrams for PLCNPs samples confirmed the results of photoluminescence and UV-vis spectra, which a logical shift in color of the photoluminescence emission was observed by an increase in the concentration of the amide groups. The PLCNPs samples have remarkable stability (in physical and optical properties) when applied on polar substrates such as polymer sheet and cellulose paper. Therefore, the PLCNPs samples were used for development of eco-friendly water based anticounterfeiting inks, photoluminescence organic light emitting diodes (OLEDs), and also the photodetection of scratches in a fast and facile manner. The printed security tags and hand-written phrases on cellulosic papers have orange fluorescent emission with maximum intensity because nanoscale size of particles, which reduced the light scattering and increased the accessible concentration of OXOH for light absorption. A coating of poly(vinyl alcohol) (PVA)/PLCNPs solution onto a blue LED (365nm) was led to a change in the color of emission from blue to purple, because of the excitation of OXOH molecules at 365nm with the subsequent emission of purple light. The photodetection of created scratch on polycarbonate sheet was carried out by spray of PLCNPs solution on sheet and then illumination with UV irradiation (365nm). Developed water based PLCNPs samples have interesting optical properties, high stability on different surfaces and nanoscale particle size which are applicable in multiple applications such as eco-friendly photoluminescent inks for anticounterfeiting technologies, photoluminescence OLEDs, and also optical detector for monitoring of scratches on different substrates.